The Milky Way is the Galaxy in which you and I find ourselves reading this webpage at the moment.
It is estimated to be some 100,000 light years in diameter, although recently we have begun to suspect that it is in fact up to 150,000 light years in diameter.
So why can’t we be entirely sure about the distance? Well for one reason it’s because we live deep within the Milky Way and there’s no way that we can travel through normal space fast enough to get out and look back and have a look. The reason we can work out how we might look is by looking at other Galaxies and comparing how their stars work, and then looking at stars within our own galaxy and building out a model.
Just a big Solar System
Essentially the Milky Way acts as a really really really really (you get the idea) Solar System just like our own. There are 200-400 billion stars within the Milky Way galaxy and they all orbit the centre of the galaxy in the same way that the Earth and the other planets orbit the sun…. and just like the size difference between us and the Sun the centre of the Milky way weighs in at a mass of 4 Million times that of the sun… but it occupies only a space the size of 1/3 of our own Solar System.
It takes the Sun 1 Cosmic Year to orbit the entire Milky Way… which is equivalent to 220 Million Earth years. Given the age of our own Sun, around 5000 Million Years, that means that our Sun is about 21 years old in Cosmic Years.
Unlike the centre of our own Solar System where we can see the Sun, we can not see what we are orbiting around when we look to the centre of our Milky Way. For one thing, there’s so many stars, gas and dust between us and the centre that we can’t use an optical telescope to see the centre, but even if we could there wouldn’t be anything there to see.
So what is it?
A Black Hole in the centre of the Milky Way
Our best guess is that there’s a black hole in the middle of the Galaxy which would explain how the starts act so close the middle, and why we can’t see anything when we look towards it.
It is suspected that several small galaxies collided together to form this super massive black hole, however it isn’t as hungry as it might be. In fact the black hole in the centre of the Milky Way only consumes 1% of the amount of gas and dust that it should be consuming but we have no idea why. It is thought that because it isn’t as greedy it isn’t producing the same amount of X-Rays that other super massive black holes create which in turn gets sent through the Galaxy killing off anything like…. well like us really.